1. Field of the Invention
The present invention relates to signal transmission apparatus for transmitting a digital (pulse) signal on a transmission line, and in particular to the signal-line structure of the transmission line.
2. Description of the Related Art
A digital signal has a complex waveform that can be analyzed as a Fourier series of sinewave components ranging from a direct-current (dc) component to a fundamental clock frequency component and higher harmonics thereof. Due to the complexity of its waveform, a digital signal cannot be transmitted through a filter circuit such as the inductor-capacitor (LC) filter circuits that are employed when only a single sinewave frequency, or a narrow band of frequencies, is transmitted. Conventional digital signal transmission apparatus uses dc coupling between the transmission line and its driver and receiver. Because of the conventional dc coupling, the dc component of the digital signal is transmitted together with the fundamental clock-frequency component and other high-frequency components. That is, dc current is drawn, consuming unnecessary power.
Relevant information about the transmission of digital signals can be found in, for example, Japanese Unexamined Patent Application Publication Nos. 11-284126, 2000-174505, and 2002-124635. Further information can be found in Otsuka, et al., “Measurement of Potential Swing by Electric Field on Package Transmission Lines,” Proceedings of ICEP, pp. 490-495 (April 2001, hereinafter, Reference 1a); Otsuka, et al., “Measurement Evidence of Mirror Potential Traveling on Transmission Lines,” Technical Digest of 5th VLSI Packaging Workshop of Japan, pp. 27-28 (December 2000, hereinafter, Reference 1b); and Otsuka et al., “Sutakkuto pea senro” (Stacked-pair lines), JIEP Journal, Vol. 4, No. 7, pp. 556-561 (November 2001, hereinafter, Reference 2). Further information was also presented in a paper at the 15th conference of the Silicon Technology research group of the Japan Applied Physics Society in a session titled “Chokosoku taso haisen gijutsu no kadai to tenbo tokushu” (Problems and prospects in ultra-high-speed multilayer interconnect technology, Feb. 18, 2000, University of Tokyo, Yamagami Hall, hereinafter referred to as the Silicon Technology conference).